我想问一下mongodb索引。我可以在查找和排序中使用不同的索引。例如，我有两个索引：
(a:-1)
(b:1,c:1)
哪些索引使用这句话？
({a:[$gt30}},{a:[$lt50}}]}.sort({c:1})
答案 0 :(得分：1)
我可以在查找和排序中使用不同的索引。
在阅读完之后，您将在文档页面底部看到索引交叉：http://docs.mongodb.org/manual/core/index-intersection/#index-intersection-and-sort
当sort（）操作要求索引与查询谓词完全分离时，索引交集不适用。
所以不，即使ypou创建了{c:1}的索引，它也无法独立地用于交叉{a:1}
哪些索引使用这句话？
在这种情况下，只会使用{a:1}。
答案 1 :(得分：0)
在名为单字段索引的单个字段上创建索引。
创建多个Single Field索引以增强查询，排序性能并没有多大帮助！您应该改用化合物索引。
查看MongoDB上的文档：https://docs.mongodb.com/manual/core/index-compound/
如果您想学习如何索引字段以及如何衡量查询的性能。
然后在YouTube上查看本教程：https://dplink.app/nxLgvk7lR
答案 2 :(得分：0)
假设我正在收集具有如下文档的人：
{
dob:
{ age : 50} ,
gender : "male" ,
phone : ""
}
现在我创建索引如下。
1 : db.persons.createIndex({"dob.age" : -1})
2 : db.persons.createIndex({phone : 1 , gender : 1})
db.persons.explain（“ executionStats”）。find（{$ and：[{“ dob.age”：{$ lt：50}}， {“ dob.age”：{$ gt：30}}]}）.sort（{gender：1}）
我将获得以下执行统计信息：
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "college.persons",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"dob.age" : {
"$lt" : 50
}
},
{
"dob.age" : {
"$gt" : 30
}
}
]
},
"queryHash" : "22FEA299",
"planCacheKey" : "5E8F38C1",
"winningPlan" : {
"stage" : "SORT",
"sortPattern" : {
"phone" : 1
},
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"dob.age" : -1
},
"indexName" : "dob.age_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"dob.age" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"dob.age" : [
"(50.0, 30.0)"
]
}
}
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1734,
"executionTimeMillis" : 10,
"totalKeysExamined" : 1734,
"totalDocsExamined" : 1734,
"executionStages" : {
"stage" : "SORT",
"nReturned" : 1734,
"executionTimeMillisEstimate" : 0,
"works" : 3471,
"advanced" : 1734,
"needTime" : 1736,
"needYield" : 0,
"saveState" : 27,
"restoreState" : 27,
"isEOF" : 1,
"sortPattern" : {
"phone" : 1
},
"memUsage" : 1914799,
"memLimit" : 33554432,
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"nReturned" : 1734,
"executionTimeMillisEstimate" : 0,
"works" : 1736,
"advanced" : 1734,
"needTime" : 1,
"needYield" : 0,
"saveState" : 27,
"restoreState" : 27,
"isEOF" : 1,
"inputStage" : {
"stage" : "FETCH",
"nReturned" : 1734,
"executionTimeMillisEstimate" : 0,
"works" : 1735,
"advanced" : 1734,
"needTime" : 0,
"needYield" : 0,
"saveState" : 27,
"restoreState" : 27,
"isEOF" : 1,
"docsExamined" : 1734,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 1734,
"executionTimeMillisEstimate" : 0,
"works" : 1735,
"advanced" : 1734,
"needTime" : 0,
"needYield" : 0,
"saveState" : 27,
"restoreState" : 27,
"isEOF" : 1,
"keyPattern" : {
"dob.age" : -1
},
"indexName" : "dob.age_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"dob.age" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"dob.age" : [
"(50.0, 30.0)"
]
},
"keysExamined" : 1734,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0
}
}
}
}
},
"serverInfo" : {
"host" : "RGGYSLT-0483",
"port" : 27017,
"version" : "4.2.0",
"gitVersion" : "a4b751dcf51dd249c5865812b390cfd1c0129c30"
},
"ok" : 1
}
这意味着首先使用IXScan在单个字段上获取数据，然后在 第三场分开。
但是当我更改查询以对已经为其创建索引的字段进行排序时，事情就发生了变化。现在{“ dob.age”：-1}索引被拒绝了。
在Mongo db中，胜出计划是一种可以提前获取100个文档的计划，而Mongo db缓存可以为查询计划。现在，将在插入1000个文档，重建索引，重新启动服务器或插入新索引后清除此缓存。
因此，将使用哪个索引取决于制胜计划。
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "college.persons",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"dob.age" : {
"$lt" : 50
}
},
{
"dob.age" : {
"$gt" : 30
}
}
]
},
"queryHash" : "DA8248FA",
"planCacheKey" : "E779554F",
"winningPlan" : {
"stage" : "FETCH",
"filter" : {
"$and" : [
{
"dob.age" : {
"$lt" : 50
}
},
{
"dob.age" : {
"$gt" : 30
}
}
]
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"gender" : 1,
"phone" : 1
},
"indexName" : "gender_1_phone_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"gender" : [ ],
"phone" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"gender" : [
"[MinKey, MaxKey]"
],
"phone" : [
"[MinKey, MaxKey]"
]
}
}
},
"rejectedPlans" : [
{
"stage" : "SORT",
"sortPattern" : {
"gender" : 1,
"phone" : 1
},
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"dob.age" : -1
},
"indexName" : "dob.age_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"dob.age" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"dob.age" : [
"(50.0, 30.0)"
]
}
}
}
}
}
]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1734,
"executionTimeMillis" : 12,
"totalKeysExamined" : 5002,
"totalDocsExamined" : 5002,
"executionStages" : {
"stage" : "FETCH",
"filter" : {
"$and" : [
{
"dob.age" : {
"$lt" : 50
}
},
{
"dob.age" : {
"$gt" : 30
}
}
]
},
"nReturned" : 1734,
"executionTimeMillisEstimate" : 0,
"works" : 5003,
"advanced" : 1734,
"needTime" : 3268,
"needYield" : 0,
"saveState" : 41,
"restoreState" : 41,
"isEOF" : 1,
"docsExamined" : 5002,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 5002,
"executionTimeMillisEstimate" : 0,
"works" : 5003,
"advanced" : 5002,
"needTime" : 0,
"needYield" : 0,
"saveState" : 41,
"restoreState" : 41,
"isEOF" : 1,
"keyPattern" : {
"gender" : 1,
"phone" : 1
},
"indexName" : "gender_1_phone_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"gender" : [ ],
"phone" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"gender" : [
"[MinKey, MaxKey]"
],
"phone" : [
"[MinKey, MaxKey]"
]
},
"keysExamined" : 5002,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0
}
}
},
"serverInfo" : {
"host" : "RGGYSLT-0483",
"port" : 27017,
"version" : "4.2.0",
"gitVersion" : "a4b751dcf51dd249c5865812b390cfd1c0129c30"
},
"ok" : 1
}